This spring ia worth the extra couple dollars - Strike Industries AR Carbine Flat Wire Spring

I bought several. they are longer than standard springs because they are flat. but the great thing is if tou want to tune your BCG recoil you can clip a 1/4" at a time. if you are under gases slightly you can clip another 1/4" These springs are so ling that I used one that I clipped to almost the same length as a factory mil spec spring for an under gased 5.56 rifle length gas system, and it amoothed it out and had no FTF or FTE. perfect. Yes I could have bought a Srpingco yellow light speing which I have done in the past for just the same darn reason. the rifle gas system has a smaller hole than it should have on both. I used pin guages to check. but it aure beats drilling out hole. for 20.00 it was a good education added to my tool chest of info. If there is noise in your rifle just plug your ears and stop being a sissy. ya maybe it twangs on some. not on mine I can't hear it. these flat springs are a great idea. now, maybe they will come up with three or four weights like springco did. I biult a spring weight tester system and check each speing I own and even the new ones. I mark them in pounds and oz. I should pattent the devise. better than using a ruler. you must be mindful of where your brass lands and how tight a pile it makes.